1. Field of the Invention
This invention relates to an electronic device constituted by use of an organic material, more particularly to an electronic device formed by the monomolecular film built-up method. Particularly, the present invention relates to electronic devices having functions of condenser, resistance element, etc.
2. Description of the Related Art
In the prior art, as the material for circuit elements, inorganic materials have been employed generally, and use of organic material has been limited only to insulating materials and dielectric materials. For forming particularly a thin film condenser among the passive elements such as resistance, condenser, etc., necessary for constituting an electronic circuit with the use of an inorganic material, there have been primarily the two methods as shown below.
(1) A dielectric thin film such as of silicon oxide, a metal oxide, etc., is formed on a metal thin film according to the method such as vacuum vapor deposition or reactive sputtering, and further a thin metal film is formed thereon.
(2) The surface of a metal thin film formed by vacuum vapor deposition is oxidized to form a dielectric layer, and metal electrodes are formed thereon.
However, the method of forming an inorganic material as the dielectric layer by the above vacuum vapor deposition or reactive sputtering is not necessarily a simple method. On the other hand, a thin film resistance has been formed in the prior art with a material such as a metal, an alloy, a metal nitride, a thermet, etc., and the resistance value is controlled by two-dimentional trimming.
However, vacuum vapor deposition or reactive sputtering, etc., which is a means for preparing a thin film resistance of the above metal material, etc., is not necessarily a simple method. Also, the range for controlling resistance value is limited.
Meanwhile, in recent years, organic materials have been actively studied, and materials exhibiting metallic conductivity in a single crystal state, and further those exhibiting ultraconductivity at extremely low temperature have been reported. Materials exhibiting the properties as a semiconductor have also been reported, and under the present situation, various electrical characteristics can be attained with an organic material solely.
Specifically, in recent years, it has been reported that an amphiphilic charge transfer complex which is an organometallic compound having tetracyanoquinodimethane (TCNQ) as the electron acceptor having a long chain alkyl group as the hydrophobic site such as bis-tetracyanoquinodimethanedocosylpyridinium can form a monomolecular film on the water surface, and a monomolecular built-up film can be prepared by building up one layer by one layer said monomolecular films (Joint Research Seminar of Insulating Materials and Electronic Materials in Formation Material 1985/11/15 p. 29). Said monomolecular built-up film has an electroconductivity as much as 0.1 S/cm in the direction parallel to the film surface, while having an electroconductivity of about 10.sup.-14 S/cm in the direction perpendicular to the film, thus being observed to behave as an insulating material.
The above monomolecular built up film is obtained according to the Langmuir-Blodgett's method (LB method; Shin Jikken Kagaku Koza (New Experimental Chemical Course), Chapter 18, p. 498-507 published by Maruzen). The basic principle of this method is as described below.
When the valance between hydrophilic property and hydrophobic property is adequate, as the molecules having a hydrophilic group and a hydrophobic group in combination are spread over a water surface and their planar density is appropriately increased, they will for a monomolecular film with hydrophilic groups directed downwardly and hydrophobic groups upwardly on the water surface. In other word, such molecules behave as the two-dimensional particle system. When the density of molecules on the surface (hereinafter referred to as a planar density) is low, it is "gaseous film" where the state equation of two-dimensional ideal gas is valid between the area per one molecule (molecule occupying area) and the surface area, while when the planar density of molecules is made higher by increasing the surface pressure, the mutual interaction between molecules is intensified, whereby the molecules become "a condensed film (or a solid film)" of a two-dimensional solid. This state has high orderliness and uniformity with fairly regular arrangement and orientation of the molecules.
The agglomerated film thus formed can be transferred onto a substrate such as glass, and by transfer of the monomolecular films for a plural number of times in layers on the same substrate, a monomolecular-built up film can be obtained. As a method for transfer onto the substrate, there have been known the vertical dipping method, the horizontal lifting method, the rotatory drum method, etc.
Such an LB method is a thin film preparation method at a normal temperature and a normal pressure, and also has the specific feature in the point that the film thickness of the built-up film can be controlled by the built-up number.
The electroconductive thin film prepared according to the above LB method is constituted of molecules having a hydrophilic site comprising a charge transfer complex, etc., and a hydrophobic site comprising a long chain alkyl group, etc. In a state of a condensed film, the hydrophilic site exhibits electroconductivity in the direction parallel to the film surface due to great overlaping of electron clouds of the charge transfer complex constituting the hydrophilic site. On the other hand, the hydrophobic site will form an insulating portion because the long chain alkyl group is insulating. Thus, the built-up film obtained on the substrate according to the above LB method has a constitution in which electroconductive portions and insulating portions are laminated alternately.
Also, formation of a PN junction semiconductor comprising a complex system of a monomolecular built-up film of a triphenylmethane type dye has been reported.
To summarize, various electrical elements are primarily formed of inorganic materials in the prior art, and there is involved the problem that extremity conditions such as a high temperature or a high vacuum are essentially required during preparation or treatment of these electrical elements.
In various electrical elements, ultramicronization and higher densification are increasingly demanded, and for accomplishing these objects, there is a limit in inorganic materials as the base material, and therefore studies have been made about utilization of organic materials. By use of these organic materials, higher densification to some thousand-fold as compared with the use of inorganic materials of micron units of the prior art is possible.
However, since extremity conditions such as a high temperature or a high vacuum in inorganic materials cannot be applied to organic materials or biological materials, no electrical element utilizing organic material or biological material has been realized yet.